Cable modems are well known in the art. A cable modem is a type of modem that provides access to a data signal sent over the cable television infrastructure. Cable modems are primarily used to deliver broadband Internet access, taking advantage of unused bandwidth on a cable television network. In 2005 there were over 22.5 million cable modem users in the United States alone.
A cable modem is a network appliance that enables high speed data connections to the internet via data services provided by the local cable company. Data from the home is sent upstream on a carrier that operates on the 5 MHz to 42 MHz band of the cable spectrum. Downstream data is carried on a 88 MHz to 860 MHz band. The cable modem system can have additional networking features such as Voice over IP (VoIP), wireless connectivity or network switch or hub functionality.
The term cable Internet access refers to the delivery of Internet service over the cable television infrastructure. The proliferation of cable modems, along with DSL technology, has enabled broadband Internet access in many countries. The bandwidth of cable modem service typically ranges from 3 Mbps up to 40 Mbps or more. The upstream bandwidth on residential cable modem service usually ranges from 384 kbps to 30 Mbps or more. In comparison, DSL tends to offer less speed and more variance between service packages and prices. Service quality is also far more dependent on the client's location in relation to the telephone company's nearest central office or Remote Terminal.
Users in a neighborhood share the available bandwidth provided by a single coaxial cable line. Therefore, connection speed varies depending on how many people are using the service at the same time. In most areas this has been eliminated due to redundancy and fiber networks.
With the advent of Voice over IP telephony, cable modems are also be used to provide telephone service. Many people who have cable modems have opted to eliminate their Plain Old Telephone Service (POTS). An alternative to cable modems is the Embedded Multimedia Terminal Adapter (EMTA). An EMTA allows multiple system operators (MSOs) to offer both High Speed Internet and VoIP through a single piece of customer premise equipment. A multiple system operator is an operator of multiple cable television systems.
Many cable companies have launched Voice over Internet Protocol (VoIP) phone service, or digital phone service, providing consumers a true alternative to standard telephone service. Digital phone service takes the analog audio signals and converts them to digital data that can be transmitted over the fiber optic network of the cable company. Cable digital phone service is currently available to the majority of U.S. homes with a large number of homes are now subscribing. The number of homes subscribing is currently growing by hundreds of thousands each quarter. One significant benefit of digital phone service is the substantial consumer savings, with one recent study saying residential cable telephone consumers could save an average of $135 or more each year.
A block diagram illustrating prior art cable and telephone access to a subscriber premises is shown in FIG. 1. The example system, generally referenced 10, comprises a subscriber premises (e.g., residence, business, etc.) 22 that is adapted to receive both cable and telephone service. Cable service is provided by the local cable provider wherein the cable signal originates at the cable head end facility 12 and is transmitted over RF cable 18 to the subscriber premise 22 where it terminates at the cable POP 28. One or more televisions, set-top boxes, or other cable ready appliances are 24 are connected to the cable box 28 via RF cable wiring 34.
Telephone service is provided by the local telephone company. Telephone 26 are connected to the telephone POP 30 via the internal 2-wire telephone wiring 32. The telephone POP is connected to the public switched telephone network (PSTN) via a local access line 20 which terminates in the nearest central office (CO) 16. Note that the system 10 thus provides cable and telephone services provided by different entities. The two systems (cable and telephone) are not related at the premises and do not depend on one another.
In many premises, an alarm system 36 is connected to the 2-wire telephone wiring. The alarm system is tied into the telephone system for use by the alarm system to dial out in the event of an alarm indication to a central monitoring station. If the phone line is currently in use when an alarm condition arises, the alarm system is operative to disconnect the call and grab the phone line for its own use. In this manner, the transmission of the alarm indication is not delayed because the phone line was in use.
Thus, in the event that the RF cable is cut, the alarm system continues to function and is still able to dial out in the case of an alarm condition. If, on the other hand, the telephone local access line 20 were cut, the alarm system would not be able to use the telephone network to dial out to the central monitoring station. When the alarm system detects the loss of the telephone line, it sounds an audible alarm and/or attempts to contact the central monitoring station via alternate means. For this reason, some residences and many businesses utilize cellular phones connected to the alarm system as an alternate communication mechanism. In the event the telephone local access line is cut, the alarm system can still dial out over the cellular phone. Note that any other wireless or alternative communications means may be used as well (e.g., RF radio, etc.).
A block diagram illustrating prior art cable only access to a subscriber premises is shown in FIG. 2. The example system, generally referenced 40, comprises a subscriber premises (e.g., residence, business, etc.) 46 that is adapted to receive service only from the local cable company (i.e. no telephone service from the local telephone company). Cable service is provided by the local cable provider wherein the cable signal originates at the cable head end facility 42 and is transmitted over RF cable 44 to the subscriber premise 46 where it enters a splitter 48. One output of the splitter goes to the televisions, set top boxes, and other cable appliances via internal cable wiring 66.
The other output of the splitter comprises the data portion of the signal which is input to the cable modem 62. The cable modem is adapted to provide both Ethernet and USB ports. Typically, a router 56 is connected to the Ethernet port. One or more network capable computing devices 52, e.g., laptops, PDAs, desktops, etc. are connected to the router 56 via internal Ethernet network wiring 54. In addition, the router may comprise or be connected to a wireless access point that provides a wireless network (e.g., 802.11b/g/a) throughout the subscriber premises.
The cable modem also comprises a subscriber line interface card (SLIC) 64 which provides the signals and functions of a conventional local loop to the plurality of installed telephone devices 60 via internal 2-wire telephone wiring 58. In particular, it generates call progress tones including dial tone, ring tone, busy signals, etc. that are normally provided by the local loop from the CO. Since the telephone deices 60 are not connected to the CO, the SLIC in the cable modem must provide these signals in order that the telephone devices operate correctly.
In a traditional analog telephone system, each telephone or other communication device (i.e. subscriber unit) is typically interconnected by a pair of wires (commonly referred to as tip and ring or together as subscriber lines, subscriber loop or phone lines) through equipment to a switch at a local telephone company office (central office or CO). At the CO, the tip and ring lines are interconnected to a SLIC which provides required functionality to the subscriber unit. The switches at the central offices are interconnected to provide a network of switches thereby providing communications between a local subscriber and a remote subscriber.
The SLIC is an essential part of the network interface provided to individual analog subscriber units. The functions provided by the SLIC include providing talk battery (between 5 VDC for on-hook and 48 VDC for off-hook), ring voltage (between 70-90 VAC at a frequency of 17-20 Hz), ring trip, off-hook detection, and call progress signals such as ringback, busy, and dial tone.
A SLIC passes call progress tones such as dial tone, busy tone, and ringback tone to the subscriber unit. For the convenience of the subscriber who is initiating the call, these tones normally provided by the central office give an indication of call status. When the calling subscriber lifts the handset or when the subscriber unit otherwise generates an off hook condition, the central office generates a dial tone and supplies it to the calling subscriber unit to indicate the availability of phone service. After the calling subscriber has dialed a phone number of the remote (i.e. answering) subscriber unit, the SLIC passes a ring back sound directed to the calling subscriber to indicate that the network is taking action to signal the remote subscriber, i.e. that the remote subscriber is being rung. Alternatively, if the network determines that the remote subscriber unit is engaged in another call (or is already off-hook), the network generates a busy tone directed to the calling subscriber unit.
The SLIC also acts to identify the status to, or interpret signals generated by, the analog subscriber unit. For example, the SLIC provides −48 volts on the ring line, and 0 volts on the tip line, to the subscriber unit. The analog subscriber unit provides an open circuit when in the on-hook state. In a loop start circuit, the analog subscriber unit goes off-hook by closing, or looping the tip and ring to form a complete electrical circuit. This off-hook condition is detected by the SLIC (whereupon a dial tone is provided to the subscriber). Most residential circuits are configured as loop start circuits.
Also connected to the cable modem 62 is the alarm system 68. The alarm system is connected to the cable modem via 2-wire telephone wiring 58. Under normal conditions, the alarm system does not know that it is not connected to a CO that is part of the PSTN. In the event that the RF cable 44 is cut or disconnected, however, not only is cable service cut off but telephone service as well. This is because the telephone voice conversations are transmitted over the RF cable using VoIP. Even though the RF cable is cut and voice calls cannot be made, the alarm system does not react by sounding an alarm and/or attempting to communicate to the central monitoring station via alternate communication means such as cellular or other wireless mechanism. This is because the SLIC in the cable modem continues to present the normal tip and ring voltage levels and telephone call progress tones. Thus, the alarm system does not know that the RF cable was cut or disconnected and cannot be used to call a central monitoring station for help. In this second example, the alarm system will alert only if the telephone wiring is cut whereby the connection between the alarm system and the cable modem SLIC is severed or disconnected.
It is thus desirable to have a mechanism that overcomes the disadvantages of the prior art by having the alarm system sound and/or communicate an alert when the RF cable to the subscriber premises is cut or disconnected.